The present invention relates to an apparatus for illuminating instrument pointers, wherein light is emitted through the pointers so as to provide better visibility.
There has been proposed so called indirect illumination for illuminating instruments having pointers, in which pointers are illuminated by light which is reflected on the inner wall of the enclosure of the instrument.
In one example of prior art pointer illuminating apparatus employing indirect illumination system for use in automobile clocks, a transparent dial board with a printed film provided on its surface is disposed to partition the interior of the enclosure, the hour hand shaft, minute hand shaft and second hand shaft driven by the clock movement located behind the dial board are passed through an opening formed in the board, and the hour hand, minute hand and second hand are mounted to the shafts in parallel to the dial board. A lamp is provided behind the dial board, and a shadow plate is attached to the periphery of a transparent front plate of the enclosure. The printed film on the transparent dial board is made up of a white lower layer and a black upper layer which is partly removed in accordance with the dial indication. In such an arrangement, part of light emitted from the lamp illuminates the entire transparent dial board. Therefore, light passing through the white layer is radiated forwardly only through the dial indication removed of the black printed layer, and thus the indication is displayed in a mild light. On the other hand, light passing through a gap between the side edge of the dial board and the interior wall of the enclosure is reflected on the interior wall of enclosure and on the back surface of the shadow plate, and illuminates the dial board and the front surface of the pointers.
Such a conventional system as described above, however, does not provide satisfactory visibility since pointers are illuminated by reflected light, and the car driver will possibly fail to read out time correctly when he glances at the clock. Moreover, when the light intensity is increased to enhance the brightness of the pointers, brightness of the dial board is also increased, which adversely affects transparence illumination of the dial board.